Re: Costly? No...
After writing COBOL code onto gridded paper on a local College programming course we were then allowed to attempt to compile it and debug it once it had been keyed in by some faceless admin member.
Our time on each terminal was limited so I used this time to do pretty much anything other than what I was supposed to do.
I discovered that you could copy in a new copy of VAX/VMS equivalent of the autoexec.bat file into anyone elses root folder so decided to see what would happen if I copied in a file containing a single command 'Logout' (or whatever the equivalent was).
Much glee was had as my fellow students were immediately logged out the next time they tried to connect.
Much less glee was had when I tested whether the same would work with the Admin account. It did.
There was quite some cursing from the tutor as he failed to log into his account for the rest of the lesson...